The invention relates to apparatus for coating the inner surface of cap-shaped substrates with a dielectric layer system. More particularly, the invention relates to coating the inner surface of reflectors with a cold light mirror coating by using a coating chamber which is defined by the cap-shaped substrate and a receiver part assembled with the dielectric layer system disposed proximate the edges and connected gastight thereto. Moreover, the invention relates to such apparatus wherein a gas intake duct and a gas exhaust duct are connected by a receiver. A displacer is used having one or more ducts to define the gas layer to be reacted, and a plasma zone is reacted in the gas layer by being excited. The invention also relates to a unit for coating cap-shaped substrates, in which several cap coating stations are placed side by side.
Coating devices of the above-described type are known from DE-OS 4008405 in which several caps are placed side by side in a grid for coating with a plasma pulse process on a bottom plate of a receiver. To keep the reaction volume as small as possible, the caps are sunk in suitable indentations in the bottom plate. The coverplate of the receiver is provided with an arrangement of displacers corresponding to the arrangement of the indentations in the bottom plate, which dip into the cavities limited by the inner surfaces of the caps to be coated. In the sidewalls of the receiver, several gas exhaust openings are provided, by which the reaction gases, depleted of laminate, can be suctioned off by a vacuum pump. This device has the drawback that the gas flow inside the receiver, on the one hand, is asymmetrical for each cap and, on the other hand, differs from cap to cap, so that, depending on the position of the cap inside the receiver, the coating can be different. Since the production tolerances do not permit an exact matching of the indentation to the cap shape, the caps are not completely supported, and a gap forms between the outside of the cap and the indentation. This can cause coating of the outside wall of the cap.
To eliminate this undesired effect, another embodiment was proposed in DE-OS 4008405 in which the cap to be coated was joined with a unilaterally open vessel to a receiver. Although the undesired deposition of the reaction gases on the outer surface of the cap is avoided with such a device, no completely symmetrical gas flow control is achieved in the area of the cap because of the gas exhaust pipe. Another drawback of this device consists in the fact that only individual caps can be coated in succession. If several such devices are operated, the latter are equipped with a separate gas generator and a separate microwave device for generating plasma. The unit and operating costs are very high due to the addition of individual coating units.